scholarly journals Thermodynamic Analysis of Supercell Rear-Flank Downdrafts from Project ANSWERS

2007 ◽  
Vol 135 (1) ◽  
pp. 240-246 ◽  
Author(s):  
Matthew L. Grzych ◽  
Bruce D. Lee ◽  
Catherine A. Finley
Keyword(s):  
Potential Temperature ◽  
Surface Wind ◽  
Thermodynamic Characteristics ◽  
General Concept ◽  
Equivalent Potential Temperature ◽  
Near Surface ◽  
Project Analysis ◽  
Equivalent Potential ◽  
Virtual Potential Temperature ◽  
Convective Inhibition

Abstract Data collected during Project Analysis of the Near-Surface Wind and Environment along the Rear-flank of Supercells (ANSWERS) provided an opportunity to test recently published associations between rear-flank downdraft (RFD) thermodynamic characteristics and supercell tornadic activity on a set of 10 events from the northern plains. On average, RFDs associated with tornadic supercells had surface equivalent potential temperature and virtual potential temperature values only slightly lower than storm inflow values. RFDs associated with nontornadic supercells had mean group equivalent potential temperature and virtual potential temperature values that were colder relative to storm inflow values than their respective tornadic counterparts. Additionally, the analysis revealed that RFDs associated with tornadic supercells had higher CAPE and lower convective inhibition than the RFDs of nontornadic supercells, on average. The results of this study provide further support for the general concept that a thermodynamic delineation generally exists between the RFDs of tornadic and nontornadic supercells.

scholarly journals Observations of the Surface Boundary Structure within the 23 May 2007 Perryton, Texas, Supercell

2011 ◽  
Vol 139 (12) ◽  
pp. 3730-3749 ◽  
Author(s):  
Patrick S. Skinner ◽  
Christopher C. Weiss ◽  
John L. Schroeder ◽  
Louis J. Wicker ◽  
Michael I. Biggerstaff
Keyword(s):  
Potential Temperature ◽  
Boundary Structure ◽  
Surface Boundary ◽  
Equivalent Potential Temperature ◽  
In Situ Data ◽  
Research And Teaching ◽  
Equivalent Potential ◽  
Virtual Potential Temperature ◽  
High Precipitation

Abstract In situ data collected within a weakly tornadic, high-precipitation supercell occurring on 23 May 2007 near Perryton, Texas, are presented. Data were collected using a recently developed fleet of 22 durable, rapidly deployable probes dubbed “StickNet” as well as four mobile mesonet probes. Kinematic and thermodynamic observations of boundaries within the supercell are described in tandem with an analysis of data from the Shared Mobile Atmospheric Research and Teaching Radar. Observations within the rear-flank downdraft of the storm exhibit large deficits of both virtual potential temperature and equivalent potential temperature, with a secondary rear-flank downdraft gust front trailing the mesocyclone. A primarily thermodynamic boundary resided across the forward-flank reflectivity gradient of the supercell. This boundary is characterized by small deficits in virtual potential temperature coupled with positive perturbations of equivalent potential temperature. The opposing thermodynamic perturbations appear to be representative of modified storm inflow, with a flux of water vapor responsible for the positive perturbations of the equivalent potential temperature. Air parcels exhibiting negative perturbations of virtual potential temperature and positive perturbations of equivalent potential temperature have the ability to be a source of both baroclinically generated streamwise horizontal vorticity and greater potential buoyancy if ingested by the low-level mesocyclone.

Interannual Variability of Monsoon Precipitation and Local Subcloud Equivalent Potential Temperature

2013 ◽  
Vol 26 (23) ◽  
pp. 9507-9527 ◽  
Author(s):  
John V. Hurley ◽  
William R. Boos
Keyword(s):  
Interannual Variability ◽  
Southern Oscillation ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Quasi Equilibrium ◽  
Equivalent Potential Temperature ◽  
Monsoon Precipitation ◽  
Relevant Variable ◽  
Near Surface ◽  
Equivalent Potential

The interannual variability of monsoon precipitation is described in the context of a convective quasi-equilibrium framework. Using two reanalysis products and two global precipitation datasets, the authors examine linear relationships between seasonal anomalies of precipitation and subcloud equivalent potential temperature (θeb) local to six monsoon regions. This approach provides a single near-surface thermodynamically relevant variable over both land and ocean, extending previous studies of interannual monsoon variability that emphasized ocean surface temperatures. After removing the variability linearly associated with an index of the El Niño–Southern Oscillation, positive monsoon precipitation anomalies are shown to be associated with enhanced θeb local to and slightly poleward of the climatological θeb maximum. The variations in continental θeb local to the monsoon precipitation maxima are mainly due to variations in subcloud specific humidity, with changes in subcloud temperature having the opposite sign. Motivated by the fact that some of these subcloud humidity anomalies occur over deserts poleward of monsoon regions, the relationship of 700-hPa flow with precipitation is examined, and enhanced precipitation in several regions is found to covary with the properties of shallow meridional circulations. The implications of these results for the understanding of monsoon interannual variability are discussed.

scholarly journals An Observational and Modeling Study of Mesoscale Air Masses with High Theta-E

2018 ◽  
Vol 146 (8) ◽  
pp. 2503-2524 ◽  
Author(s):  
Wolfgang Hanft ◽  
Adam L. Houston
Keyword(s):  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Vertical Motion ◽  
Model Analysis ◽  
Equivalent Potential Temperature ◽  
Near Surface ◽  
Air Mass ◽  
Warm Sector ◽  
Equivalent Potential ◽  
Modeling Study

Abstract Typically, the cool side of an airmass boundary is stable to vertical motions due to its associated negative buoyancy. However, under certain conditions, the air on the cool side of the boundary can undergo a transition wherein it assumes an equivalent potential temperature and surface-based convective available potential energy that are higher than those of the air mass on the warm side of the boundary. The resultant air mass is herein referred to as a mesoscale air mass with high theta-e (MAHTE). Results are presented from an observational and mesoscale modeling study designed to examine MAHTE characteristics and the processes responsible for MAHTE formation and evolution. Observational analysis focuses on near-surface observations of an MAHTE in northwestern Kansas on 20 June 2016 collected with a Combined Mesonet and Tracker. The highest equivalent potential temperature is found to be 15–20 K higher than what was observed in the warm sector and located 2–5 km on the cool side of the boundary. This case was also modeled using WRF-ARW to examine the processes involved in MAHTE formation that could not be inferred through observations alone. Model analysis indicates that differential vertical advection of equivalent potential temperature across the boundary is important for simulated MAHTE formation. Specifically, deeper vertical mixing/advection in the warm sector reduces moisture (equivalent potential temperature), while vertical motion/mixing is suppressed on the cool side of the boundary, thereby allowing largely unmitigated insolation-driven increases in equivalent potential temperature. Model analysis also suggests that surface moisture fluxes were unimportant in simulated MAHTE formation.

scholarly journals The Creation of a High Equivalent Potential Temperature Reservoir in Tropical Storm Humberto (2001) and Its Possible Role in Storm Deepening

2012 ◽  
Vol 140 (2) ◽  
pp. 492-505 ◽  
Author(s):  
Klaus P. Dolling ◽  
Gary M. Barnes
Keyword(s):  
High Surface ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Surface Wind ◽  
Tropical Storm ◽  
Equivalent Potential Temperature ◽  
Equivalent Potential ◽  
Global Positioning ◽  
Vortical Hot Towers ◽  
The Creation

Thirty global positioning system dropwindsondes (GPS sondes) were used to identify and examine the creation of a reservoir of high equivalent potential temperature (θe) in the nascent eye of Tropical Storm Humberto (2001). The θe did not increase in the high surface wind portion of the storm as it does in mature hurricanes; instead air spiraled into the light-wind center of the developing storm where it was trapped by subsidence under a mesoscale convectively generated vortex (MCV). An energy budget revealed that the inflow column took 7 h to reach the storm center during which a combined average surface enthalpy flux of ~230 W m−2 was diagnosed via the bulk aerodynamic equations. This estimate is close to the 250 W m−2 required for balance based on the energy acquired by the column. The high θe in the lowest kilometer, overlain by a near dry-adiabatic layer under the anvil base, resulted in convective available potential energy (CAPE) exceeding 2500 m2 s−2. This conditionally unstable air later served as fuel for the convection within the nascent eyewall. The authors speculate that CAPE of such a large magnitude could accelerate the updraft and stretch the vorticity field, essentially turning garden-variety cumulonimbi into the vortical hot towers argued by several researchers to play a role in tropical cyclone formation and intensification.

scholarly journals Surface Analysis of the Rear-Flank Downdraft Outflow in Two Tornadic Supercells

2008 ◽  
Vol 136 (7) ◽  
pp. 2344-2363 ◽  
Author(s):  
Brian D. Hirth ◽  
John L. Schroeder ◽  
Christopher C. Weiss
Keyword(s):  
Data Collection ◽  
Thermodynamic Properties ◽  
Surface Analysis ◽  
Potential Temperature ◽  
Heavy Precipitation ◽  
Equivalent Potential Temperature ◽  
Equivalent Potential ◽  
Virtual Potential Temperature ◽  
Horizontal Variations

Abstract The rear-flank downdraft regions of two tornadic supercells were sampled on 12 June 2004 and 9 June 2005 using four “mobile mesonet” probes. These rear-flank downdraft outflows were sampled employing two different data collection routines; therefore, each case is described from a different perspective. The data samples were examined to identify variations in measured surface equivalent potential temperature, virtual potential temperature, and kinematics. In the 12 June 2004 case, the tornadic circulation was accompanied by small equivalent potential temperature deficits within the rear-flank downdraft outflow early in its life followed by increasing deficits with time. Virtual potential temperature deficits modestly increased through the duration of the sample as well. The 9 June 2005 case was highlighted by heavy precipitation near the tornado itself and relatively small negative, or even positive, equivalent and virtual potential temperature perturbations. Large horizontal variations of surface thermodynamic properties were also noted within several regions of this rear-flank downdraft outflow.

What Is the Representation of the Moisture–Tropopause Relationship in CMIP5 Models?*

2015 ◽  
Vol 28 (12) ◽  
pp. 4877-4889 ◽  
Author(s):  
Yutian Wu ◽  
Olivier Pauluis
Keyword(s):  
Annual Cycle ◽  
Seasonal Cycle ◽  
Climate Models ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
Equivalent Potential Temperature ◽  
Near Surface ◽  
Equivalent Potential ◽  
Extratropical Tropopause

Abstract A dynamical relationship that connects the extratropical tropopause potential temperature and the near-surface distribution of equivalent potential temperature was proposed in a previous study and was found to work successfully in capturing the annual cycle of the extratropical tropopause in reanalyses. This study extends the diagnosis of the moisture–tropopause relationship to an ensemble of CMIP5 models. It is found that, in general, CMIP5 multimodel averages are able to produce the one-to-one moisture–tropopause relationship. However, a few biases are observed as compared to reanalyses. First of all, “cold biases” are seen at both the upper and lower levels of the troposphere, which are universal for all seasons, both hemispheres, and almost all CMIP5 models. This has been known as the “general coldness of climate models” since 1990 but the mechanisms remain elusive. It is shown that, for Northern Hemisphere annual averages, the upper- and lower-level “cold” biases are, in fact, correlated across CMIP5 models, which supports the dynamical linkage. Second, a large intermodel spread is found and nearly half of the models underestimate the annual cycle of the tropopause potential temperature as compared to that of the near-surface equivalent potential temperature fluctuation. This implies the incapability of the models to propagate the surface seasonal cycle to the upper levels. Finally, while reanalyses exhibit a pronounced asymmetry in tropopause potential temperature between the northern and southern summers, only a few CMIP5 models are able to capture this aspect of the seasonal cycle because of the too dry specific humidity in northern summer.

What are the Best Thermodynamic Quantity and Function to Define a Front in Gridded Model Output?

2019 ◽  
Vol 100 (5) ◽  
pp. 873-895 ◽  
Author(s):  
Carl M. Thomas ◽  
David M. Schultz
Keyword(s):  
Real Time ◽  
Potential Temperature ◽  
Thermodynamic Quantity ◽  
Kinematics And Dynamics ◽  
Horizontal Gradient ◽  
Model Output ◽  
Equivalent Potential Temperature ◽  
Thermal Front ◽  
Equivalent Potential ◽  
Definition Of

AbstractFronts can be computed from gridded datasets such as numerical model output and reanalyses, resulting in automated surface frontal charts and climatologies. Defining automated fronts requires quantities (e.g., potential temperature, equivalent potential temperature, wind shifts) and kinematic functions (e.g., gradient, thermal front parameter, and frontogenesis). Which are the most appropriate to use in different applications remains an open question. This question is investigated using two quantities (potential temperature and equivalent potential temperature) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) from both the context of real-time surface analysis and climatologies from 38 years of reanalyses. The strengths of potential temperature to identify fronts are that it represents the thermal gradients and its direct association with the kinematics and dynamics of fronts. Although climatologies using potential temperature show features associated with extratropical cyclones in the storm tracks, climatologies using equivalent potential temperature include moisture gradients within air masses, most notably at low latitudes that are unrelated to the traditional definition of a front, but may be representative of a broader definition of an airmass boundary. These results help to explain previously published frontal climatologies featuring maxima of fronts in the subtropics and tropics. The best function depends upon the purpose of the analysis, but Petterssen frontogenesis is attractive, both for real-time analysis and long-term climatologies, in part because of its link to the kinematics and dynamics of fronts. Finally, this study challenges the conventional definition of a front as an airmass boundary and suggests that a new, dynamically based definition would be useful for some applications.

scholarly journals MSE Minus CAPE is the True Conserved Variable for an Adiabatically Lifted Parcel

2015 ◽  
Vol 72 (9) ◽  
pp. 3639-3646 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Potential Energy ◽  
Thermodynamic Equilibrium ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Equivalent Potential Temperature ◽  
Moist Static Energy ◽  
Neutral Buoyancy ◽  
Equivalent Potential ◽  
Nonhydrostatic Pressure ◽  
Static Energy

Abstract For an adiabatic parcel convecting up or down through the atmosphere, it is often assumed that its moist static energy (MSE) is conserved. Here, it is shown that the true conserved variable for this process is MSE minus convective available potential energy (CAPE) calculated as the integral of buoyancy from the parcel’s height to its level of neutral buoyancy and that this variable is conserved even when accounting for full moist thermodynamics and nonhydrostatic pressure forces. In the calculation of a dry convecting parcel, conservation of MSE minus CAPE gives the same answer as conservation of entropy and potential temperature, while the use of MSE alone can generate large errors. For a moist parcel, entropy and equivalent potential temperature give the same answer as MSE minus CAPE only if the parcel ascends in thermodynamic equilibrium. If the parcel ascends with a nonisothermal mixed-phase stage, these methods can give significantly different answers for the parcel buoyancy because MSE minus CAPE is conserved, while entropy and equivalent potential temperature are not.

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